Release 7.4.2: Limit indexes with VARCHARs to max. size of 255 bytes for MySQL v5.6 server support

[Guest]

Root cause description:
With MySQL v5.6 and above VARCHAR fields used in an INDEX/KEY need to be explicitly limited by the amount of bytes used for the INDEX/KEY.

Solution description:
Explicitly limit VARCHAR field in affected INDEX/KEY;
e.g. INDEX () -> INDEX (, (255))

Moreover the affected INDEX has been corrected to also include the context identifier

Resolved state: fix
Assessment: none
Test cases: Manually tested against a deployed MySQL v5.6 server
Version: v7.4.2
Git commit: 5352e775f1c551bd4ebc0c5cffe3f5cfe12ec616
Git repository: backend
Git branch: release-7.4.2
Bundle name: c.o.server/c.o.admin
Package name: core/admin